Inertial navigation systems (INS) are used in civil and military aviation, missiles and other projectiles, submarines and space technology as well as a number of other vehicles. INSs measure the position and attitude of a vehicle by measuring the accelerations and rotations applied to the system's inertial frame. INSs are widely used because it refers to no real-world item beyond itself. It is therefore resistant to jamming and deception.
An INS may consist of an inertial measurement unit combined with control mechanisms, allowing the path of a vehicle to be controlled according to the position determined by the inertial navigation system. An inertial measurement unit contains instruments for position monitoring. Often typical INS uses a combination of accelerometers and any number of control devices.
INSs have typically used either gyrostablized platforms or ‘strapdown’ systems. The gyrostabilized system allows a vehicle's roll, pitch and yaw angles to be measured directly at the bearings of gimbals. The INS is traditionally rotated using electromagnetic motors on a ball bearing supported gimbal axis. A disadvantage of this scheme is that it employs multiple expensive precision mechanical parts. It also has moving parts that can wear out or jam, and is vulnerable to gimbal lock. In addition, for each degree of freedom another gimbal is required thus increasing the size and complexity of the INS. Therefore, to get complete three dimensional calibration, at least three gimbals is needed.
INSs require periodic rotation to calibrate instruments. There is a need for rotational control of INSs without the use of conventional torque motors eliminating complex parts that add weight, size and cost to the INS assembly. A traditional method of rotating an INS for calibration is to torque it about an axis using electromagnetic motors on a ball bearing supported gimbal axis. A disadvantage of this method is that it employs multiple expensive precision mechanical parts. It also has moving parts that can wear out or jam, and is vulnerable to gimbal lock. Another problem of this system is that for each degree of freedom another gimbal is required thus increasing the size of the inertial system.
INSs using ball bearing supported gimbals typically contain embedded instrumentation, such as acceleromaters. In these systems, data from the instrumentation supported by the gimbals is communicated to other systems through moving contact devices, such as slip rings, which provide a constant electrical channel for data without restricting the movement of the inertial sensor assembly. However, slip rings, like ball bearing supported gimbals, are moving physical structures subject to wear and therefore represent a potential failure point for an inertial navigation system, or other system. Data signals communicated through slip rings also suffer from noise interference and low bandwidth. The embedded instrumentation also limits the full rotational capacity of the INS due to the physical constraints of the connection.
Another type of inertial navigation system is one that floats a sensor assembly with neutral buoyancy in a fluid. This method requires an extremely complex assembly, sensitive temperature control and obvious sealing challenges that add considerably to the cost of deployment and maintenance. Also, many of these fluids are hazardous or require a high degree of purity.
Inertial navigation systems which use spherical gas bearings typically require very tight tolerances on the surrounding support shell. These tight tolerances increase the cost of the system and limit the design flexibility of the system.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a guidance system which is inexpensive and easy to move in all directions for calibration without having parts that wear out or require extensive maintenance.